For many years, foot health professionals have used pink Plastazote® as the standard material for the top layer of foot orthotics for diabetic patients. One of the primary reasons it is widely considered to be the safest and best material for this layer of foot orthotics is the lack of residual chemicals.
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| Figure 1 |
Plastazote foam is produced with only pure nitrogen. Other foams use chemical blowing agents, which leave behind residual chemicals such as ammonia and urea. Even low levels of these residual chemicals can present a risk of irritation or allergic reaction to the diabetic patient's foot. The level of chemicals present in cross-linked foams typically exceeds acceptable levels listed in the Code of Federal Regulations for repeated food contact (United States Government, 2003).
This means that just as these chemicals can cause problems when absorbed into the body through food, they can cause a risk when absorbed through the skin, especially when ulcers or other wounds are present.
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| Figure 2 |
In tests conducted, P-Cell and Plastacell-P provide better compression set and shock absorption but are nearly twice the bulk density as pink Plastazote, which would explain most of the property differences. Their broad cell size distribution is typical of foams produced using chemical blowing agents. Also in Table I, other high-density materials are shown which would give better compression set resistance, less pack-down, and better cushioning than both P-Cell and Plastacell-P.
While beneficial, shock absorption is not the primary goal of the top layer of a diabetic orthotic--conformance is. Several experiments (see Figure 1) measuring the conformance of pink Plastazote were performed in athletic and business shoes simulating the typical use of foot orthotics. The experiments demonstrated the benefits of this near-the-skin top layer by providing soft comfort, shock absorption, rapid conformance, and protection to the immediate skin. Previously published data shows P-Cell and Plastacell-P's higher densities would slow conformance on compression set. Since the rapid conformance of Plastazote is most desirable for the top layer of the orthotic for a diabetic foot, claims that P-Cell compresses less than pink Plastazote can be misleading when choosing the most appropriate material to use.
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| Figure 3 |
Pink Plastazote continues to be the material of choice for foot health professionals, because, as we stated previously, it is foamed with only pure nitrogen. This eliminates potentially irritating chemicals, thus limiting the risk to your patients. It is also an industry standard because the top layer conforms rapidly to the individual foot, providing a glove-fit which limits rubbing retarding potential blister or callus formation. The thicker, stiffer foams and gels used on the lower parts of the orthotic will provide additional shock absorption for the foot.
In general, but especially when trying to minimize the risk of potential infection for diabetic patients, the cleanest foams with the best conformance rates should be used in the top layer of foot orthotics. Heavier density materials are not the safest choice for use with foot orthotics for diabetic patients and are best utilized for shock absorption in lower layers.
Professionals in the healthcare arena have a responsibility to use the safest and most appropriate material in the care of their patients. For more than 30 years, pink Plastazote has been proven the best material for the top layer of foot orthotics, and it continues to be the most trusted choice.
Robert W. Keller, PhD is President of Zotefoams Inc., Walton, Kentucky.
References
Sax, N.I. Dangerous Properties of Industrial Materials. 6th Ed., Van Nostrand Reinhold. New York. 1984. p. 340.
United States Government (2002). 21CFR 177.1520. In (Ed.),Code of Federal Regulations, Part 21 (Rev. ed. 2002). Washington, DC: US Government Printing office.
Marty, R. 2003 – Data Supports Use of P-cell in Diabe Footwear. Biomechanics, X(3), 69.
